N Matthew 21:2-7, you can read about the fulfillment of the exact prophecy that we find tucked quietly away in here Zechariah 9:9. Jesus, as Savior and King, did indeed ride into Jerusalem on a donkey just as this prophet foretold. Now, perhaps many have ridden into Jerusalem on donkeys, I do not know, but they didn't come with salvation as Christ did. Zechariah prophesied that this One would bring salvation with Him. Jesus did that. He was a poor and lowly carpenter, but He was also the perfect Son of God. A week after His entrance, He was pouring out His blood on a wooden cross; providing for the rescue of Israel, and of us.
Once more, we must remind ourselves concerning who exactly was in Zechariah's immediate audience. What was important to the construction workers to whom he made his address? Well, consider the more obscure content of Zechariah's sermon here. Notice the naming of the many cities and peoples that surrounded Israel. In their weak position in Jerusalem, perhaps one of the primary concerns of the post-exilic Jews was the hostile Gentiles that lived all around them? They certainly were looking forward to a day when they would be safe in their land. The idea of a strong king standing up in Jerusalem again would have been one of the most appealing ideas that could have possibly been postulated in Zechariah's day. And, indeed, this is exactly what Zechariah did speak about.
Now, while it should be admitted that the Jews wanted (and still want) a Messiah to step in with deliverance politically, militarily and economically, Zechariah indicated that what Israel needed most was a spiritual Savior. It is true that Israel needed material and practical peace, but what they needed first was a spiritual revival. Jesus of Nazareth did what was necessary for them to have just that.